1. Field of Invention
This invention pertains to the receiver section of a modem used in data communication, and more particularly, to a receiver incorporating a Viterbi decoder without the need for special processors dedicated for trellis decoding.
2. Background of the Invention
Digital data is frequently exchanged over communication channels using wireline modems. It is commercially advantageous to operate these modems at very high speeds and at lower signal-to-noise ratios. Therefore, various schemes have been devised for improving the performance of standard modems at lower signal-to-noise ratios. One such scheme, commonly known as trellis encoding, involves the use of redundant data bits used to generate a preselected allowable number of data sets. At the receiver, the redundant bits are used to correct errors in the received signals. It has been found that trellis encoding provides a gain of at least 4db in the signal-to-noise ratio of the data signals received by wireline modems. However, prior art trellis decoding or Viterbi decoding schemes involve a large number of calculations and memory which must be performed in external, relatively large capacity processors. Therefore, there is a need for a Viterbi decoder which uses a simpler decoding scheme, requiring a relatively smaller data processor. Such a decoder would be especially advantageous in a microprocessor-based modem in which the resident microprocessor could also be used for Viterbi decoding, thereby eliminating the need for an external processor.